(1). Field of the Invention
The present invention relates to a display device that forms an image on the basis of image data received, and particularly to a display device that presents an image on the basis of a synchronizing signal of image data received.
(2). Description of the Related Art
There has been known a display device, such as television receiver, that is connectable to an image-data generating apparatus through a connector. Image data is outputted from the image-data generating apparatus to the display device, and an image based on the image data is presented on a screen of the display device. For instance, the image data generating apparatus may be a personal computer or a home video game machine.
FIG. 5 is a block diagram of the known display device. The display device 1 receives image data and displays an image based on the image data. The display device 1 includes a video-signal control circuit 2 and an image display unit 3. The video-signal control circuit 2 generates a RGB image signal on the basis of the image data received and the image display unit 3 presents an image on the basis of the image signal generated by the video-signal control circuit 2. The image data generated by the image-data generating apparatus is outputted through a cable 4 to the video-signal control circuit 2 so that the image is presented on the image display unit 3.
The video-signal control circuit 2 obtains a horizontal synchronizing signal and a vertical synchronizing signal from the image data received, and outputs the image signal to the image display unit 3 when the values of the obtained synchronizing signals correspond to values stored or registered in advance. The registered values of the horizontal and vertical synchronizing signals are set within a range that is determined depending on the capability or specification of the image display unit 3 and that of the video-signal control circuit 2.
Generally, resolution, pixel clock, and synchronizing signals are parameters defining presentation of image, and within a range there are an indefinitely large number of combinations of specific values of the resolution, pixel clock, and synchronizing signals. Accordingly, within a range there are an indefinitely large number of resolution values that the video-signal control circuit 2 support, in theory. However, the resolution at which an image is presented basically depends on the resolution of the image display unit 3 as operated in a normal display mode. Therefore, in the known display device the video-signal control circuit 2 implements an adjustment such as handling two pixels as one pixel, in order to resolve a conflict in resolution between the video-signal control circuit 2 and the image display unit 3. It is noted that the term “pixel clock” refers to an update frequency at which a color signal inputted to each pixel is updated when an image is displayed.
JP-A-2006-72363 teaches a method of reconciling a resolution conflict between a video-signal control unit and a display unit. That is, according to the method, when the resolution of image data received is higher than that of the display unit, the resolution of the image data is decreased so as to enable the display unit of the lower resolution to present an image based on the image data.
JP-A-11-15425 teaches a method of simplifying an operation required for a user to reconcile a resolution conflict between a video-signal control unit and a display unit. More specifically, when an image signal of a resolution that differs from the resolution of the display unit is to be presented, the user can make a resolution adjustment in a simplified manner, that is, the user directly can adjust the resolution of the display unit by switching the resolution at the side of the display unit.
JP-A-2000-305529 teaches a method according to which when there occurs a resolution conflict between a video-signal control unit and a display unit, a user is informed of this fact. That is, when the resolution of an image signal obtained is higher than the resolution of the display unit, a message indicating this fact is presented on the display unit.
However, according to the known techniques described above, when the resolution of the image data desired to be presented does not correspond to any of the registered values, the image can not be presented on the screen. Further, in order to widen the range of the values of the resolution of the image data capable of presentation to enable the display unit to present image data of any resolution value, it is required to predefine and store or register an indefinitely large number of combinations of values of the resolution of the video-signal control circuit, values of the synchronizing signals, and values of the pixel clock. For instance, where the above-described combinations, or correspondences among the resolution values and the values of the other parameters, are stored in a storage medium, the capacity of the storage medium should be sufficiently large to be capable of storing all the data of the combinations or correspondences.